Apple's new iPhone 6S Plus looks just like last year's 6 Plus -- but looks in this case are highly deceiving. While the 2014 model represented a major new step in design and performance, this year's version, which arrived on Sept. 25, delivers changes to just about everything you can't see.

Existing features of the 6S Plus (and its smaller sibling, the 6S) have been improved and there are even a few groundbreaking features thrown in for good measure.

Look and feel

The iPhone 6S Plus looks just like its predecessor: A smooth aluminum casing curves to meet the glass-covered front with the display framed in white or black; for the case, you now have the choice of Rose Gold along with the previous colors of Space Gray, Silver and Gold.

The Home button, which also doubles as the Touch ID fingerprint scanner, still sits centered at the bottom of the display. The power button remains on the right side, with volume buttons and a mute switch on the left. The latest models are slightly heavier and slightly thicker: The 6 Plus was 0.28 in. thick and weighed 6.07 oz. while the 6S Plus is 0.29 in. thick and weighs 6.77 oz. It's not much, but you can feel the difference. (The iPhone 6S is now 0.28 in., which is .01 in. more than last year's model, and weighs 5.04 oz., as compared to last year's 4.55 oz.)

The new case uses 7000 Series aluminum and has been strengthened at the points where last year's models were susceptible to bending.

Apple also used a dual ion-exchange process on the glass for the new display that, Apple execs say, increases the strength. The glass shields a 4.7 in. (for the 6S) or 5.5 in. (for the 6S Plus) Retina display, with 1334 x 750 pixels at 326 pixels per inch (PPI) crammed into the smaller display, and 1920 x 1080 pixels at 401 PPI in the larger iPhone. I was able to compare my iPhone 6S Plus to a 6S owned by a co-worker; both are bright and show off a great range of colors without overdoing saturation.

Working in concert with updated software and a brand new Taptic Engine is the 3D Touch function. 3D Touch isn't new to Apple; it debuted earlier this year on the Watch as Force Touch and on Apple's MacBook and MacBook Pro laptop trackpads. It's an effective way to interact with the iPhone: Any type of pressure on the glass is measured by the capacitive sensors, and specific actions can be triggered based on how hard you press down.

And it's cleverly integrated throughout the operating system. (Note: 3D Touch is a feature only available on the new iPhones. iOS 9 may run on the previous generations, but only the new phones support this feature, which Apple is specifically touting in new TV ads.)

3D Touch in-depth

There are a variety of scenarios in which 3D Touch can make a difference. Let's say you want to message a friend. The usual steps are tap to open the Messages app; go back a step to the main friend list; scroll through the list; tap the friend; type the message. To do the same on an iPhone with 3D Touch, you press firmly on the Messages icon on the Home Screen, and a list of the three friends you last messaged appears; below the list is an option to start a new message.

If you want to mark your parking spot, you normally tap to open the Maps app; tap the triangle to the lower left to get a lock on your position; tap to the lower right to open the Options drawer; and then tap Drop a Pin to mark your location. With 3D Touch, you press firmly on the Maps app on the Home Screen and tap Mark My Location. Done. (There are also quick shortcuts for Search Nearby, Send My Location and Directions Home.)

Apple's done selfie-takers a solid with this one. To take a selfie shot from the Home Screen in an iPhone without 3D Touch, you tap open the Camera app, swipe to Photo mode, tap on the Switch Camera toggle at the upper right, and then tap the shutter button. With 3D Touch, you press firmly on the Camera app on the Home Screen and select Take Selfie. (Other options include Record Video, Record Slo-mo and Take Photo.)

Most of the apps that come with the iPhone have support for 3D Touch from the Home Screen and each is contextually sensitive: Calendar will let you quickly add an event, Safari will let you start a Private browsing session immediately and the Phone app lets you call your top three favorites. Third-party apps are now starting to support this feature, including Instagram and Facebook. (The latter's quick shortcuts include taking a photo/video, uploading an existing photo/video and a quick link for writing a post.)

Peek, Pop and other 3D Touch features

3D Touch brings with it a number of other new features.

First off, there's Peek and Pop -- and despite the cutesy names, they are pretty powerful new actions. Peek lets you view the contents of an email or text message from its respective list without actually having to open the message.

To activate Peek, apply a bit more pressure to the item you want to see in that list; the iPhone will give haptic feedback to acknowledge the press and a preview of the item will appear. If this is something that requires no further attention, ease up on the pressure and the window will slide into the list again so you can continue scrolling.

By swiping up on the Peek view, you can see related actions: Swiping up in Messages will let you "Mark as Read" or send a quick or custom message; in Mail, swiping lets you reply, forward or mark or move a message, or set up notifications for that email thread.

Pop is simply full screen mode to Peek's preview. Press a little harder and the content expands to fit the entire display, with the haptic feedback to accompany it.

I found Peek and Pop to be quite useful, especially in text messages. I'm always receiving links to interesting videos or interesting websites from friends. Peek and Pop let me check out what they send without actually leaving the Messages app. And if the content truly is interesting, then I press the screen a little harder and the content takes over what I was doing. Peek and Pop also work in Safari, letting you preview websites before committing to the link. It's brilliant.

3D Touch can also be used to switch apps. Start by pressing firmly on the left side of the screen; dragging a bit to the right will bring up the App Switcher and firmly swiping all the way to the right switches to the last app.

When editing text, a deep press on the keyboard enables trackpad mode, which lets you place the cursor exactly where you want quickly and accurately. Also, moving the cursor over a word and then pressing firmly again will highlight that word; pressing firmly twice selects a block of text. You can drag your finger up and down to select and highlight more text.

Interestingly, while there are quite a few areas in which you can find 3D Touch, there is a curious spot where you can't. While on the Apple Watch, you can clear out every Notification at once with a firm press on the Notifications screen, you can't do that on the iPhone. You still have to close Notifications by hand. That's not a deal-breaker by any stretch, but it would be nice to activate a Clear All via firm press.

There are all sorts of ways to take advantage of 3D Touch, and it's not just limited to built-in apps. Developers can also use the tech for their games, and there are drawing apps that change the sketch based on the pressure you use while you draw. Under Wallpaper in Settings, there are now nine choices in the Live section, six of which are beta fish in three black and three white backgrounds; the remaining three are variations of clouds/smoke. Select any of these for the lock screen and they'll animate when pressed.

Live Photos

That brings us to Live Photos. When this feature is enabled -- by tapping the circle icon dead center on the top of the Camera app -- and you take a still image, the phone also records video and audio from a second-and-a-half before you took the picture and a second-and-a-half after. When you press on the photo that was created with Live Photo, the result is something straight out of Harry Potter: Photos that animate a bit before settling back into a still image.

In practice, the effect is sometimes really cool -- other times, it's clear that the video isn't at the same resolution as the image and the 15 frames-per-second (fps) video comes across choppy and jumpy. In my initial look at the iPhone 6S Plus, I said that I wished Live Photos were 24fps and a little higher quality. After spending more time with the feature, I also wish the transition used wasn't a fade/dissolve. It's too jarring, given the high quality of the images and video the new iPhone is capable of.

One last thing: Live Photos can be used on the lock screen and, like Apple's Live Wallpapers, can be animated with a press. Also, if you're on an iPhone and receive a Live Photo -- say, from a text message or email -- you can still see the animation by pressing and holding the photo even if you don't have 3D Touch.